1. Field of the Invention
The present invention relates to a negative-type polymerizable composition and a planographic printing plate precursor. More specifically, the invention relates to a negative-type polymerizable composition and a planographic printing plate precursor that are highly sensitive to and writable by an infrared laser.
2. Description of the Related Art
Conventional panographic printing plate precursors in widespread use are PS plates having a structure in which a lipophilic photosensitive resin layer is provided on a hydrophilic support. In the production process thereof, a desired printing plate is usually obtained by performing mask exposure (surface exposure) via a lith film followed by dissolution and removal of non-image areas. In recent years, digitalization technology, in which image information is electronically processed, stored, and output using a computer, has become widespread. Thus, a variety of new image outputting methods that can accommodate such digitalization technology has been put to practical use. Consequently, there is strong demand for a computer to plate (CTP) technique in which scanning is conducted according to digitalized image information using light having high directivity, such as a laser beam, to thereby directly produce a printing plate without using the lith film. Therefore, obtaining a planographic printing plate precursor that can comply with such techniques has become an important technical issue.
As a type that is subjected to scanning exposure, the planographic printing plate precursor comprising a hydrophilic support having disposed thereon a lipophilic photosensitive resin layer (hereinafter referred to as “photosensitive layer”) that contains a photosensitive compound capable of generating active species such as a radical or a Broensted acid upon laser exposure has been proposed, and has already been put on the market. This planographic printing plate precursor is scanned by a laser beam according to digital information such that active species can be generated. The action of the generated species causes a physical or chemical change in the photosensitive layer, which leads to insolubility of the layer. The layer is then subjected to development processing to thereby obtain a negative-type planographic printing plate. Particularly, from a planographic printing plate precursor comprising a hydrophilic support having disposed thereon a photopolymerizable photosensitive layer containing a photopolymerization initiator which exhibits excellent sensitizing speed, an ethylenically unsaturated compound which is addition-polymerizable and a binder polymer which is soluble in an alkaline developer, and optionally a protective layer which has an oxygen blocking property, from the standpoints of high productivity, simple development processing, and excellent resolution and inking, a preferable printing plate having excellent printing performance can be obtained.
Conventional binder polymers used to constitute the photosensitive layer are an organic macromolecular polymer capable of being developed by alkali, e.g., methacrylic acid copolymers, acrylic acid copolymers, itaconic acid copolymers, crotonic acid copolymers, maleic acid copolymers and partially esterified maleic acid copolymers (refer to Japanese Patent Application Publication (JP-B) No. 59-44615, Japanese Patent Application Publication (JP-B) Nos. 54-34327, 58-12577 and 54-25957, JP-A Nos. 54-92723, 59-53836, 59-71048 and 2002-40652).
However, in conventional planographic printing plate precursors provided with a photosensitive layer containing such a binder polymer, the developer permeates into a part of image areas where curing is insufficient, and consequently, damages are incurred in the photosensitive layer leading to lowered printing durability. In order to cope with this problem, an attempt to suppress permeation of the developer into the image area was made. However, this attempt sacrificed developing properties in non-image areas. Therefore, it was very difficult to achieve both suppression of permeation of the developer into image areas and superior developing properties in non-image areas.